Plasma CNC ohmic sensor / tool height control

Metal Shop
#1

After pierce I saw the tool height decreasing until it collided with the part. I did not see any warping in the metal.

After cleaning the shield and checking the spade connection on the sensor, I used the “Ohmic sensor” light on the control software and a wire to debug. It lit when the shield was connected to the slat.Before it started the arc for the second path it threw an error; the sensor was lit but the torch wasn’t touching anything. When I removed the shield I noticed a buildup of slag on the aperture of the shield, which was causing the shield to make contact with the nozzle. I cleaned it off but it was back again in one cut!

Stuff:

  • I used the shield and swirl ring that was on the machine
  • I used my own nozzle and electrode\
  • I tried different cut heights from 0.06" to 0.066"
  • I left the pierce height at default 0.110" (I think)
  • I increased the time delay from initial > cut height 0.0s to 0.5s
  • I decreased the feed rate from 190 ipm to 172 ipm
  • The ohmic sensor light worked fine once I cleaned the buildup
  • 65A nozzle, 10 gauge mild steel, other settings at library default

When I turned off the THC it worked fine.

#2

I had same issue last week, couldnt keep it from diving into the part with Torch Height Control enabled. I had a lot of short cuts so voltage was swinging widely. I want to try some longer cuts to see if the arc voltage is stable.

#3

That ohmic sensor is by far the most common error with the dynatorch. You need to check every connection from the wire to the torch tip to make sure it’s all tight and touching. Otherwise the torch won’t fire

#4

There is a ohmic sensed. torch height controller. I am curious is the error when there is a short or no resistance between two terminals of the ohmic probes. Or is the error signal infinite resistance between two terminals of the ohmic probe… Also is there two separate terminals to the ohmic probe(I.E. positive and negative). Or is one of the probes terminals tide to a positive rail or negative rail for the tool height controller?

Separately…

This is an upgrade idea for the hypertherms dynatorch. I believe this could improve things by providing linuxcnc as a operating system.

#5

The THC effectiveness is comprised by the build up of dross(slag) & the differential reference to ground. We have seen a potential difference between the ground rod & electrical building ground of 30 volts.